Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 132135
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
335 PM MDT Thu Jul 13 2017

.SHORT TERM...(This evening through Friday)
Issued at 115 PM MDT Thu Jul 13 2017

Upper high starting to expand nwd over Wyoming with warm mid level
temps and limited convection potential. Still some lower level
moisture hanging in the ern zones and we could still see a storm
fire in mainly Johnson County but nothing like yesterday (even
though the nern corner is in marginal). A few storms off the Uintas
will still have the potential to skim the srn Sweetwater County
border. As the upper high shifts ever so slightly off to the east
(more straight to our south), it will allow some limited mainly mid
level moisture to rotate/lift nwd into our wrn zones overnight.
Ahead of this moisture, there is a weak disturbance also moving ne
towards wrn Wyoming and sounding do some some small capes (couple
hundred Joules) so it`s possible we`ll see a few storms form later
this afternoon or evening in the far west. The odds increase on
Friday as disturbance and associated moisture over NV lift nwd then
newd across us later tonight into Friday.  Not a significant deep
layered surge but this time of the year it doesn`t take much to aid
in more convection, especially during max heating time and into the
evening. So idea of wdly sct/sct mtn storms Friday with a few across
the lower elevations, especially in and near the foothills and sern
zones seems good and no changes made there. Moisture hangs around
overnight so there will likely be some showers/slgt chance of
thunder over and near the mountains and probably a few weak showers
even across the lower elevations at times overnight Friday. On
Saturday, another plume skims our nwrn corner while some of the
Friday moisture remains east of the divide. Most of the convection
looks to be in the nrn two-thirds of the area so no changes to going
forecast. Sct higher elevations showers/tstms and isold lower
elevations. On Sunday, approaching shortwave and cold front may act
on another plume in the ssw mid level flow and aid in some stronger
storms in YNP and surrounding area. Added in some hail wording up
there instead of just the gusty wind wording. Otherwise, isold
storms just about anywhere with the far ecntrl zones having the
least chance. Still quite warm to hot through the period though with
only some clouds and outflows helping at times.

.LONG TERM...(Friday night through Thursday)
Issued at 115 PM MDT Thu Jul 13 2017

With the ridge axis moving to the east over the Plains and a
secondary high building slightly over the desert southwest, the
northern Rockies into WY will see more of a SW-NE mid-level flow as
the active storm track drops a bit southward.  The forecast pattern
should also allow some return flow from the Plains into eastern WY
as well as a slight decrease in 700mb temperatures.  Overall, enough
moisture and instability will continue the afternoon and evening
showers and thunderstorms from Monday through Thursday.  Some weak
disturbances may also enhance the storminess on a couple of days,
though details are a bit vague at this time.  The models are
suggesting that late Wednesday could be one of those times. The
northern and eastern areas should see a couple of pushes of cooler
air from Montana. Afternoon high temperatures are expected to drop
slightly to near normal or just above normal, with morning lows
still above normal. Sustained gradient wind is not expected through
the period, though thunderstorm outflows could create gusts of 30-40
mph.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 330 PM MDT Thu Jul 13 2017

VFR conditions continue to be forecast through the period, with a
slight chance of MVFR under and around any thunderstorms. Isolated
showers and thunderstorms have developed on the Bighorn Mountains
and over Johnson County late this afternoon, and should continue
through 02Z/Fri. Some early evening storms may move into far western
WY from eastern ID as well, but not very confident in impacting
KJAC. The primary hazard with these high-based showers and
thunderstorms will be erratic wind gusts 30-40 knots. Otherwise,
prevailing surface winds will be generally light, less than 15 knots
across the area. A disturbance from the Great Basin will wrap around
the high and skirt northwestern WY Friday, bringing a chance of
showers to the KJAC area, then spreading eastward through the day by
increasing instability and moisture. By early to mid afternoon
Friday, thunderstorms should develop over much of the mountain areas
and move to the ESE.  The stronger storms could develop from KBYG to
KCPR to KRKS.  East of the divide should also see a northeasterly
surface push in the afternoon.

&&

.FIRE WEATHER...
Issued AT 115 PM MDT Thu Jul 13 2017

Fuels are now at critical levels for most forecast zones east of the
Divide (Please see the Fire Weather Forecast product for more
information). Through Saturday, fire danger will be low to moderate
for most mountain locations...elevated for all other lower
elevations due to very warm to hot daytime temperatures and low
humidity levels. Winds, however, will continue relatively light
across the entire forecast area today through Saturday. The only
exception will occur near any shower/storm where winds could briefly
gust 35 mph or more. Today, mainly isolated precipitation chances
will be found along/near and south of a Casper Mountain to Evanston,
WY line while Friday and Saturday the emphasis for isolated/widely
scattered showers/storms will mainly occur over/near the area`s
mountains or a weak surface boundary/front stretching through
central Wyoming.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...Skrbac
LONG TERM...McDonald
AVIATION...McDonald
FIRE WEATHER...Skrbac



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